Pulmonary information transmission system

ABSTRACT

A system by which signals pertaining to the pulmonary condition of a patient are transmitted to a location which is remote from the location of the patient. The signals are transmitted as the patient is being tested. pulmonary information in the form of spirometry data and total lung capacity volume are transmitted by means of telephone lines or the like to a location remote from the patient, and at the remote location the transmitted information may be studied by a person who is well acquainted in the art of analysis of such information. Patients at various locations provide information to a central location at which studies of the information are conducted. Thus, a specialist in the art of such studies is in a position to receive information from various patients who may be located at numerous widespread places and who may be many miles from the specialist.

United States Patent [19 1 Griffis et al. Apr. 10, 1973 PULMONARYINFOTION OTHER PUBLICATIONS TRANSMISSION SYSTEM Med. & Biol.Engineering, Vol. 9, pp. 247-254, Per- [75] Inventors: Roy A. Griffis;L. Thomas Rautergamon Press, 1971.

kus; Terence Torzala, all of Dayton,

Journ. of Assoc. for Advancement of Med. Instrumen- Ohio tation, Vol. 5,No. 4 July-Aug, 1971, pp. 220-223.

[73] Assignee: Systems-Research Laboratories, Inc., PrimaryExaminer'-Kyle Howell Trans-Med Systems Inc., both of AttorneywwilliamJaCOX et Dayton, Ohio, part interest to each [57] ABSTRACT [22] Filed:Sept. 20, 1971 A system by WhlCh signals pertaining to the pulmonary[21] AppI- 182,053 condition of a patient are transmitted to a locationwhich is remote from the location of the patient. The 52 us. c1...12s/2.0s, 23/254 E, 73/23 R, Signals are transmitted as the patient isbeing tested- 7 R 128/21 A pulmonary information in the form ofspirometry data 51 Int. Cl. ..A61b 5/08 and total lung capacity volumeare transmitted by [58] Field of Search ..12s/2.0s,2.07, 2.1- A; meansof telephone lines or the like to a location 23/254 R, 254 73/23, 4215remote from the patient, and at the remote location the transmittedinformation may be studied by a per- [56] References Cited son who iswell acquainted in the art of analysis of such information. Patients atvarious locations provide UNITED STATES PATENTS information to a centrallocation at which studies of 3,527,205 9/1970 Jones ..128/2.08 themfmmatw t f T i i m 3,082,761 3/1963 Engelder ..12s 2.07 the P of such Fa recewe 3 649 199 3/1972 Littlejohn ..23/230B from Vamus Patten who mayQ at 3:527:206 9/1970 Jones ..12s 2.0s numerous Widespread Places andwho y be y miles from the specialist.

22 Claims, 11 Drawing Figures l7 PRECISION e 10, 2. I

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sum 2 BF 4 know FORCED VITAL CAPAClTY FIG-2+ FUNCTIONAL RESIDUALCAPACITY FIG-3 "FIG -5 PATENTEU APR 1 0 ms SHEET 3 0F 4 NMN PULMONARYINFORMATION TRANSMISSION SYSTEM BACKGROUND OF THE INVENTION Thisinvention relates to pulmonary testing and more particularly to apulmonary testing system for transmitting pulmonary data to a centrallocation.

In the past, tests related to the pulmonary condition of a patient havebeen observed by a doctor or other specialist at the location of thepatient. The system of this invention provides means by which a doctoror other specialist can receive by telephone lines pulmonary test datafrom various locations, any of which may be remote. For example,patients tested by the specialist may be in cities remote from thelocation of the doctor or other specialist.

So far as is known, systems now in use which transmit more than one typeof pulmonary test data employ more than one pair of telephone lines.

SUMMARY OF THE INVENTION In accordance with one preferred embodiment ofthe invention, there is provided a pulmonary testing system forproviding an electrical signal indicating the peak percent of nitrogenexpired by a person in a breath and the total nitrogen mass orv volumeexpired by the person during repetitious breathing comprising meansresponsive to the persons repetitious breathing for providing a firstelectrical signal proportional to the gas flow in each exhaled breath,analyzer means'responsive to the repetitious exhaling of the person forproviding a second electrical signal indicating the percent of nitrogenduring each exhalation, integrating means responsive to the first andsecond electrical signals for providing a third electrical signalindicating the total amount of nitrogen exhaled by the person, pulsegenerator means responsive to the second electrical signal for providinga series of pulse signals, each pulse signal indicating the peak percentof nitrogen during a single exhalation, and means for providing a systemsignal by superimposing the series of pulse signals upon the thirdelectrical signal such that the series of pulse signals occur during thetime an inhalation occurs.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram showing asystem of this invention for transmission of pulmonary information.

FIG. 2 is a portion of a chart showing the results of a typicalspirometry test of a patient tested by the circuitry of this invention.

FIG. 3 is a portion of a chart showing peak nitrogen and functionalresidual capacity data of a patient tested.

FIGS. 4 11 are schematic wiring diagrams of portions of the electricalcircuitry of this invention.

DETAILED DESCRIPTION OF THE INVENTION This invention provides means bywhich a single pair of telephone lines is employed to transmitspirometry, the percentage of nitrogen present in each expired breath ofa patient, and to transmit a signal which is proportional to nitrogenvolume or mass, for the determination of functional residual lungcapacity (FRC) of the patient.

As shown in FIG. 1, a test unit 8 includes a flowmeter 10, preferably amass flowmeter, which is shown as having connected thereto a fluidconduit member 12 which is adapted to cover the nose and/or mouth of apatient, for communication with the patients respiratory system.

The flowmeter I0 provides an electrical output signal which isproportional to a derivative of the volume or mass of the expiredbreath. A suitable flowmeter, for example, is a device sold byDatametrics Corporation and referred to as In-line Flow Transducer,Series 1000. A switch arm 18 is connected to the input of a transmitter22 and when connected to a contact point 19, the flowmeter 10 iselectrically connected to the transmitter 22. Preferably, thetransmitter 22 is a frequency modulation transmitter, preferably havingan output frequency in the general range of 1300 hertz. However, atransmitter of another frequency may also be satisfactory. Theconnection of the switching arm 18 to a contact 15 joins a precisionoscillator 17 to the transmitter 22. The transmitter 22 is joined to astart-stop switch 24, which is connected to a telephone circuit 30. Thetelephone circuit 30 may be a full duplex system and includes a pair ofwires or lines. The precision oscillator 17 is used to test thetelephone circuit 30. Also joined to the telephone circuit 30 is asignal filter 32 to which is connected an alarm 34.

The telephone circuit 30 extends to a central receiver unit 40 withinwhich is a demodulator 42 connected to the telephone circuit 30. Thecentral receiver unit 40 may be very remote from the test unit 8.

Also within the central unit 40 and joined to the telephone circuit 30is a signal switch 44. Also within the central receiver unit 40 is anintegrator and special purpose computer 45, and a chart recorderinstrument 48 which is connected to the integrator and special purposecomputer 45. The chart recorder 48 is also connected to the demodulator42.

Also within the test unit 8 and joined to the fluid conduit 12 is afluid conduit 60, which, through a valve 62, is connected to a source ofoxygen 64. Also connected to the fluid conduit 12 is a fluid conduit 68which through a valve 70, is connected to a nitrogen percent analyzer72. A suitable analyzer may for example, be such a device sold byMed-Science Company and referred to as Model 505 Nitralyzer.

The output of the flowmeter 10 is joined by a conductor to one input ofan analog multiplier 76, shown schematically in FIG. 4, and to the inputof a minimum flow detector 78, shown schematically in FIG. 5. Thenitrogen percent analyzer 72 is connected by a conductor 77 to a secondinput of the multiplier 76, by a conductor 79 to the signal input of apeak percent nitrogen follower 80, shown schematically in FIG. 6, and bya conductor 81 to the input of a. minimum percent nitrogen detector 82,shown schematically in FIG. 7. The multiplier 76 has an output connectedby a conductor 83 to a multiplier output gate 84, shown schematically inFIG. 8. The multiplier 76 may be any suitable instrument which iscapable of multiplication of two analog quantities. The multiplier 76employed herein is an instrument produced by Hybrid Systems andidentified as 107C Transconductance Multiplier and is shown in FIG. 4 ashaving a gain adjustment 89 and a balance adjustment 91 connectedthereto. The

multiplier 76 also has an X terminal, a Y terminal, and a Z terminal.

The peak percent nitrogen follower 80 has an output connected by aconductor 85 to a percent nitrogen sample pulse generator 88, shownschematically in FIG. 9. The percent nitrogen sample pulse generator 88includes time delay circuitry. The minimum flow detector 78 is connectedby a conductor 73 to a first inhibit input of the multiplier output gate84. The minimum percent nitrogen detector 82 is connected by a conductor71 to a second inhibit input of the multiplier output gate 84 and to aninhibit input of the percent nitrogen sample pulse generator 88. Thepercent nitrogen sample pulse generator 88 has output conductors 67 and69 connected to clear and read inputs of the peak percent nitrogenfollower 80.

An integrator 94 shown schematically in FIG. 11, is connected by aconductor 95 to one input of a summer device 92 and receives a signalthrough a conductor 97 from the multiplier output gate 84. A pair ofconductors 103 connects the switch 24 to control inputs of theintegrator 94. The summer device 92 is connected by a conductor 99 to aswitch contact 96 which is joined through switching arm 18 to thetransmitter 22. A conductor 101 connects the percent nitrogen samplepulse generator 88 to a second input of the summer device 92.

A breath switch 100 is connected to the input to the transmitter 22 andto a breath light 102. The breath switch 100 is any suitable switchwhich, when receiving a signal directly or indirectly from the flowmeter10, causes the breath light 102 to become energized.

OPERATION The circuitry of this invention includes means fortransmission of spirometry test data as the patient exhales into thefluid conduit 12.

Prior to testing a patient, the switching arm 18 is placed in contactwith the switch contact 15, and the precision oscillator 17 applies atest signal to the transmitter 22, which in response thereto applies afrequency modulated signal through the switch 24 to the flowmetertelephone circuit 30, and to the demodulator 42 of the central receiverunit 40 for calibration of these elements.

During the spirometry test, the valves 62 and 70 are closed so that allof the expired breath from the patient flows into the flowmeter 10, andthe switching arm 18 is placed in contact with the switch contact 19.

The flowmeter provides an electrical signal which is transmitted throughthe switch contact 19 and the switching arm 18 to the transmitter 22.The breath switch 100 senses that an expired breath of the patient hascaused a signal to be applied to the transmitter 22, and the breathswitch 100 causes the breath light 102 to become energized to indicateto the operator that the patient's expiration is causing a signal to beapplied to the transmitter 22. The start stop switch 24, when closed,for example by manual operation, permits a signal from the transmitter22 to flow through the telephone circuit 30 to the demodulator 42 in thecentral receiver unit 40. The analog signal which is received from thedemodulator 42 by the integrator and special purpose computer 45 isintegrated with respect to time and the output of the integrator andspecial purpose computer 45 flows to the chart recorder 48. A signalfrom the demodulator 42 simultaneously flows directly to the chartrecorder 48.

The upper portion of FIG. 2 is a portion of a chart illustrating forcedexpiratory flow of the patient, and the lower portion of FIG. 2 is aportion of a chart illustrating the integration of the flow to providevolume of the patients forced exhalation.

When an operator at the central receiver unit 40 wishes to contact theoperator at the test unit 8, for example, to indicate that the test iscompleted, the operator uses the signal switch 44 to apply a signal of adifferent frequency to the telephone circuit 30, and this signal isdetected by the signal back filter 32 which activates the signal backalarm 34. The operators at both units can then connect telephones to thetelephone circuit 30 for telephone communication between the test unitlocation of the patient and the central receiver unit 40.

The circuitry of this invention is also employed to transmit to thecentral receiver unit 40 information regarding the percent nitrogen ineach expired breath of a patient and nitrogen volume, to determine totallung volume and functional residual capacity of the patient. These testsare referred to as nitrogen washout" tests. These tests are based uponthe fact that air normally contains approximately eighty percentnitrogen, and it is assumed that the patients lungs normally contain airhaving this percentage of nitrogen.

For these tests, the valves 62 and are opened and the switching arm 18is placed in contact with switch contact 96. The patient and expires andexpires through the fluid conduit member 12. The valve 62 permits flowof oxygen from the source 64 only when the patient is inhaling. Thus,the patient inhales pure oxygen from the source of oxygen 64. Thepatient exhales into the fluid conduit 12 and the exhaled breath issensed by the flowmeter 10. A very small portion of the exhaled breathflows through the fluid conduit 68 to the nitrogen percent analyzer 72.An electrical output signal having an instantaneous magnitudeproportional to expiratory flow travels from the flowmeter 10 throughthe conductor to the multiplier 76, and an electrical signal having amagnitude, proportional to the percentage of nitrogen in the expiredbreath travels through the conductor 77 from the nitrogen percentanalyzer 72 to the multiplier 76 and through the the conductor 79 to thepeak percent nitrogen follower 80.

During this test, each inspiration by the patient contains pure oxygenand each expiration contains a percentage of nitrogen. As inspirationand expiration continue, the percentage of nitrogen in each expiredbreath should decrease.

The multiplier 76 thus receives a signal proportional to the expiratoryflow and multiplies therewith a signal proportional to the percent ofnitrogen in the expired breath, and a resultant signal output of themultiplier 76 (nitrogen flow) travels to the multiplier output gate 84.

The minimum flow detector 78, which is also joined to the multiplieroutput gate 84, provides a signal to the multiplier output gate 84 onlywhen a signal above minimum flow is received from the flowmeter 10. Theminimum percent nitrogen detector 82 provides a signal to the multiplieroutput gate 84 only when the percentage of nitrogen in an expired breathis above a given minimum value. The multiplier output gate 84 isdisabled and thus does not transmit a signal from the multiplier 76 tothe integrator 94 unless there is a signal received from the minimumflow detector 78 that an expired breath is occurring and a signal fromthe minimum percent nitrogen detector 82 that the percentage of nitrogenis above a given minimum.

The integrator 94 thus provides a signal proportional to nitrogen volumein the expired breath. The output signal of the integrator 94 istransmitted through the summer device 92 to the transmitter 22 and thentransmitted over the telephone circuit 30 to the central receiver unit40. The integration appears on the chart recorder 48 in a manner similarto that represented by a reference numeral 105 in FIG. 3.

The peak percent nitrogen follower 80 detects the peak percentage ofnitrogen in each expired breath. This peak signal is transmitted to thepercent nitrogen pulse generator 88, which includes time delaycircuitry. After the percent nitrogen, as detected by the percentnitrogen detector 82, falls below a predetermined minimum during thenext inspiration of pure oxygen, and after a given time delay, forexample, one hundred and fifty milliseconds or the like, the time delaycircuitry transmits this signal to the summer device 92, and the peaksignal travels through the summer device 92 to the transmitter 22 andtravels over the telephone circuit 30 to the central receiver unit 40.The peak signals are superimposed upon the integration signals at thechart recorder 48 in the manner illustrated by a reference numeral 107in FIG. 3.

Thus, it is understood that the peak signals 107 are transmitted to thecentral receiver unit 40 during the time that the patient is inhalingand the integration of the exhalation is transmitted to the centralreceiver unit 40 during the exhalation period. Thus, the signalscorresponding to peak percentage of nitrogen and signals pertaining tofunctional residual capacity of the patient are transmitted to thecentral receiver unit 40 over a voltage applied to one of the X or Yterminals and zero volts applied to the other of the X or Y terminals,the output of the multiplier 76 is not zero but is a positive voltageslightly above zero. In addition, the zero adjustment ofthe output asset by the balance potentiometer 91 has a slight drift. To limit theerror due to this nonideal behavior, the multiplier output gate 84 isemployed, into which the output signal from the multiplier 76 isconnected. The multiplier output gate 84, shown in FIG. 8, includes acoil 194 which operates a normally closed relay contact 196, throughwhich the multiplier output signal is applied to the integrator 94. Wheneither the flow or percent nitrogen of the patients expired breath isbelow a predetermined value, the coil 194 is energized and the relaycontact 196 is open. This occurs between expired breaths and after thenitrogen is completely washed out of the patients lungs.

The multiplier output gate 84 includes a transistor 192 having agrounded emitter, and a collector which is connected through a coil 194to a source of positive voltage V. The conductors 71 and 73 are coupledsingle pair of telephone lines, and the information received at thecentral receiver unit 40 appears on the chart in a manner such as thatillustrated in FIG. 3.

Details of portions of the system will now be discussed.

A first sample exhalation is actually taken before the first inhalationof pure oxygen, and should indicate that 80 percent nitrogen was presentin the air of the conduit 12 immediately before the beginning of thetest. When the first inhalation of pure oxygen is made, a samplenitrogen pulse indicating 80 percent nitrogen should be generated. Thismay serve as a check on the adjustment of the nitrogen analyzer 72 andmay serve as a check to indicate if oxygen was present in the breathingtube before the test began.

Conductors 103 extending from the start-stop switch 24 to the integrator94 are momentarily shorted to discharge or reset a capacitor 221 of theintegrator 94, shown in FIG. 1 1.

As stated above, the multiplier output gate 84 is disabled when theminimum flow detector 78 detects a flow signal below a minimum value orwhen the minimum percent nitrogen detector 82 detects a nitrogen levelless than a minimum value. The reason for this is that the multiplier76, shown in FIG. 4, is not ideal. With a together through respectiveforward biased diodes 188 and 190 to the base of transistor 192.Whenever a positive voltage appears on either of the conductors 71 or73, resulting from detection of the respective minimum percent nitrogenor minimum flow, the transistor 192 becomes conductive. This allowscurrent to fiow through the coil 194, opening relay contact 196. A diode198 is coupled in parallel with the coil 194 and allows the coil 194 todischarge after the transistor 192 again becomes non-conductive.

The minimum flow detector 78, as shown in FIG. 5, includes anoperational amplifier 200 operated in the inverting mode with thebase-emitter junction of a transistor 202 in the feedback loop thereof.The inverting input to the operational amplifier 200 is coupled to theconductor 75 through a resistor 204, and to a source of negative voltageV, through resistors 205 and 206. The junction of resistors 205 and 206is coupled to ground through a resistor 207. The resistors 204, 205, 206and 207 are selected so that whenever the voltage on the conductor 75 isbelow a minimum voltage, a negative voltage is applied to the invertinginput of the operational amplifier 200, and otherwise a positive voltageis applied thereto.

A positive voltage reverse-biases the emitter-base transistor junction202, causing the feedback impedance to become extremely high, and theoperational amplifier 200 attempts to saturate positively. However, theemitter-base transistor junction 202 breaks down at a voltage beforesaturation occurs. The negative current from a negative voltage iscancelled when the positive voltage applied on the conductor 75 reachesa sufficiently high value. When the total input Y voltage increases to avalue greater than the threshold,

the output of the operational amplifier 200 becomes negative as a resultof the net positive current at the negative input. This negative outputforward-biases the emitter-base transistor junction 202, and the outputof the operational amplifier 200 becomes slightly negative. Thus, aslong as the voltage on the conductor is above a minimum value, theoutput voltage of the minimum flow detector 78 which appears on theconductor 73 is near zero volts, and when the voltage appearing on theconductor 75 falls below the minimum voltage, the output voltage on theconductor 73 becomes substantially positive.

The minimum percent nitrogen detector 82, illustrated in FIG. 7functions in substantially the same manner as the minimum flow detector78. The nitrogen threshold is a small percentage of full nitrogenvolume. The minimum percent nitrogen detector 82 includes an operationalamplifier 208, having a base-emitter transistor junction 209 in thefeedback loop thereof. The operational amplifier 208 has a filtercircuit 210 in the output thereof, which makes possible smooth outputvoltage shifts as changes in nitrogen levels occur above and below thetrigger threshold of the detector circuit.

The output of the multiplier 76 is connected through the conductor 83,the multiplier output gate 84, and the conductor 97 to the input of theintegrator 94. The integrator 94, as shown in FIG. 11, includes anintegrating operational amplifier 220 having a capacitor 221 in thefeedback loop thereof. The integrator 94 also includes a unity gaininverter 224 which corrects for polarity change which occurs within theoperational amplifier 220. The gain of the integrator 94 may, forexample, be such that at the output conductor 95 thereof 1 volt equals 1liter. The input signal on line 97 to the integrator 94 is a voltageproportional to nitrogen flow in liters per minute, and the output ofthe integrator 94 is nitrogen volume in liters. The gain of theintegrator 94 is adjusted by adjusting a potentiome' ter 228 at theinput of the operational amplifier 220.

The output conductor 95 of the integrator 94 is connected to the summerdevice 92, shown in FIG. 10, which inverts the output signal of theintegrator 94 and superimposes upon the output signal of the integrator94 the signal received through the conductor 101 from the percentnitrogen pulse generator 88. The output of the summer device 92 thentravels through the conductor 99, the switch contact 96, and switchingarm 18 to the transmitter 22, as stated above.

The peak percent of nitrogen in each expired breath is determined by thepeak percent nitrogen follower 80, shown in FIG. 6. This includes anoperational amplifier 230, having the base-emitter junction of atransistor 240 and an operational amplifier 232 in the feedback loopthereof. The peak percent nitrogen follower 80 also includes anoperational amplifier 234. The output voltage of the operationalamplifier 230 is applied through the transistor 240 and through a closedsample relay contact 242 to a storage capacitor 236. When the inputvoltage appearing on the conductor 79 of the operational amplifier 230begins to decrease, the output voltage thereof does not decrease becausethe baseemitter junction of the transistor 240 in the negative feedbackcircuit of the operational amplifier 230 is reverse-biased by the valueof the previous higher voltage stored in the storage capacitor 236. Inorder for the storage capacitor 236 to maintain the charge, theimpedance looking back into the operational amplifier 230 must beextremely high. The operational amplifier 232, having a very high inputimpedance, is employed for this purpose and, as shown and discussedabove, is in the feedback loop of the operational amplifier 230. Use ofthe transistor 240 as a diode serves to reduce to a negligible value anyleakage in this portion of the circuitry.

The operational amplifier 232 serves as a voltage follower buffer withan input impedance on the order of 10 ohms in the negative feedback loopof the operational amplifier 230.

The negative feedback loop is the output loop, because the input to theoperational amplifier 230, which is an inverter, is a positive voltage,for example, 10 volts full scale with 100 percent nitrogen. In addition,the base-emitter junction of a transistor 238 and the transistor 240 areused as diodes, with the base being coupled to the collector. Since thebase-emitter transistor junctions begin leakage at a voltage somewhatbelow actual breakdown, the gain of the operational amplifier 230 isreduced to about one-fifth in order to keep this leakage valuenegligible. This attenuation is compensated for by a gain created in anoutput buffer stage which includes the operational amplifier 234,operating in a known manner, to provide the peak percent nitrogen signalto the conductor 85.

When the nitrogen level value exceeds the threshold of the minimumpercent nitrogen detector 82 during an exhalation, the logic circuitryin the percent nitrogen sample pulse generator 88 causes a positivevoltage to appear on the conductor 69, thereby rendering a transistor262 conductive and energizing a relay coil 241, shown in FIG. 6, tocause the normally open relay contact 242, which is located between theoperational amplifier 230 and the storage capacitor 236, to close. Thispermits the capacitor 236 to charge up to a peak voltage.

When the nitrogen level goes below the minimum threshold duringinhalation of pure oxygen by the patient, the voltage ceases to beapplied on the conductor 69, the transistor 262 becomes non-conductiveand the coil 241 becomes deenergized and permits the relay contact 242to open, and a voltage proportional to the peak nitrogen value is storedby the storage capacitor 236.

The storage capacitor 236 is connected to the input of the operationalamplifier 234 which has a high impedance input to minimize capacitordischarge.

After the voltage manifesting the nitrogen level at the input conductor81 falls below the threshold of the minimum percent nitrogen detector82, there is a slight delay for a reason discussed below, and then thepercent nitrogen sample pulse is generated on conductor 101 by percentnitrogen pulse generator 88. Immediately after this, a normally-closedrelay contact 252, in the peak percent nitrogen follower 80, which hadbeen open to allow peak nitrogen sampling and storage, is closed by thelogic in the percent nitrogen sample pulse generator 88, causing zerovoltage to appear on the conductor 67, thereby rendering a transistor260 non-conductive and deenergizing a coil 250 for closure of thecontact 252. The contact 252 remains in the closed position for aboutmilliseconds to allow discharge of capacitor 236. The capacitor 236 isthen in a condition to be recharged to a new peak value during the nextexhalation.

As previously stated, the percent nitrogen pulse generator 88 functionsin close conjunction with the peak percent nitrogen follower 80. Theprimary control input signal to the pulse generator 88 is the minimumpercent nitrogen detector 82 signal appearing on the conductor 71. Whenthe output of the minimum percent nitrogen detector 82 is a low voltage,indicating that the nitrogen level is above the minimum threshold, aNAND gate 258 within a NAND gate unit 259 of the percent nitrogen pulsegenerator 88, shown in FIG. 9, provides a positive voltage to theconductor 69 to energize the coil 241 of the peak percent nitrogenfollower 80 shown in FIG. 6, and closes the contact 242, therebyconnecting the output of the operational amplifier 230 to the storagecapacitor 236. During this time, the contact 252 is maintained in anopen condition, because the coil 250, associated therewith, is energizedthrough the operation of another NAND gate 261 in the NAND gate unit259.

In order for the contact 252 to be held open, a series of monostablemultivibrators 270, 272, and 274 of the percent nitrogen samplegenerator 88 shown in FIG. 9, are in the zero state, and a functionswitch 280 is in the FRC (Functional Residual Capacity) position. As thepatient exhales the nitrogen from his lungs, a voltage.

proportional to the peak nitrogen is stored by capacitor 236 in the peakpercent nitrogen follower 80. When the patient stops exhaling and againbegins inhalation of pure oxygen, the minimum percent nitrogen detector82 provides a positive voltage on the conductor 71. However, because theoutput voltage of the filter 210 in FIG. 7 rises slowly, the outputvoltage provided by a buffer circuit 288 rises slowly. This permits theNAND gate 258 to provide a near zero voltage to the conductor 69, thusdeenergizing the relay coil 241 and permitting the contact 242 to open.The zero relay contact 252, however, is still open, because themonostable multivibrators 272 and 274 are still in the low state.However, the leading edge of the output pulse on the conductor 71 fromthe minimum percent nitrogen detector 82 triggers the monostablemultivibrator 270 through the buffer 288. The time constant of thismonostable multivibrator 270 is selected so that the output thereofprovides a positive voltage for about 150 milliseconds. In addition, themonostable multivibrator 270 is not actually triggered until about 350milliseconds after the output signal on the conductor 71 from theminimum percent nitrogen detector 82 becomes positive. This is becauseof the slow rise of the output voltage of the minimum percent nitrogendetector 82 and the buffer 288. The trailing edge of the output pulse ofthe monostable multivibrator 270 triggers the monostable multivibrator272. Therefore, from the time the nitrogen level goes below thethreshold until the monostable multivibrator 272 fires, about one-halfsecond has elapsed. It is this monostable multivibrator 272 whichrenders a transistor 294, shown in FIG. 9, conductive, thereby allowingcurrent to flow through a coil 296 and moves a contact 298 connected tothe conductor 101 from a ground connection to connection with theconductor 85 from the output of the peak percent nitrogen follower 80.This generates a peak percent nitrogen sample pulse about 75milliseconds in duration in the percent nitrogen sample pulse generator88, which is connected through the conductor 101 to the second input ofthe summer device 92. The pulse is then superimposed on the functionalresidual capacity represented by reference numeral 105 and is shown bythe reference numeral 107 in FIG. 3.

The trailing edge of the monostable multivibrator 272 triggers themonostable multivibrator 274 which also has a time constant selected togenerate a pulse 75 milliseconds in duration. The output of themonostable multivibrator 274 is transmitted to the NAND gate 261, whichprovides a positive voltage to the conductor 67, to the relay coil 250,through a transistor 260, as shown in FIG. 6. When the monostablemultivibrator 274 is in its high state and the function switch 280 is inthe PRC position, the signal provided to the conductor 67 is near zerovolts, so the relay coil 250 is deenergized, and the relay contact 252closes. This discharges the peak nitrogen storage capacitor 236 andprepares the peak percent nitrogen follower 80 for the next exhalation.

As soon as the minimum percent nitrogen detector 82 again provides a lowvoltage to the conductor 71, indicating that the nitrogen level is abovethe minimum, the signal provided by the NAND gate 258 to the conductor69 becomes positive and the sample relay contact 242 closes again andthe cycle repeats.

When the subject is completely "washed out" of nitrogen, the minimumpercent nitrogen detector 82 no longer detects nitrogen above theminimum threshold during exhalation, and therefore the voltage onconductor 71 remains positive.

At this point, the sample relay contact 242 remains open and noadditional percent nitrogen sample pulses are generated. In addition,the multiplier output gate relay contact 196 remains open and noadditional functional residual capacity integration will occur.

Thus, the operator in the central receiver unit 40 knows that functionalresidual capacity computation is complete.

When the functional residual capacity computation is complete, afunction switch 282, shown in FIG. 1, is put in its grounded position.This grounds the nitrogen inputs to the multiplier 76, minimum percentnitrogen detector 82, and peak percent nitrogen follower 80. This causesthe minimum percent nitrogen detector 82 to apply a positive voltage tothe conductor 71 which holds the relay contact 196 open, thus preventingan output signal from the multiplier 76. This also holds the samplerelay contact 242 open which, together with the closed relay contact252, maintains the peak percent nitrogen follower ready for the firstsample of the next test. The relay contact 252 is closed, because thecoil 250 is deenergized as a result of the low voltage provided by theNAND gate 261 as controlled by the function switch 280.

Although the preferred embodiment of the system has been described, itwill be understood that within the purview of this invention, variouschanges may be made in the form, details, circuitry components, thecombination thereof and mode of operation, which, generally stated,provide a system capable of performance in the manner disclosed anddefined in the appended claims.

The invention having thus been described, the following is claimed:

1. A pulmonary testing system for providing an electrical signalindicating the peak percent nitrogen eitpired by a person in a breathand the total nitrogen volume expired by said person during repetitiousbreathing comprising:

means responsive to said persons repetitious breathing for providing afirst electrical signal proportional to the gas flow in each expiredbreath,

analyzer means responsive to the repetitious exhalin g of said personfor providing a second electrical signal indicating the percent ofnitrogen during each exhalation,

integrating means responsive to said first and second electric signalsfor providing a third electrical signal indicating the total volume ofnitrogen exhaled by said person,

pulse generator means responsive to said second signal for providing aseries of pulse signals, each pulse signal indicating the peak percentof nitrogen during a single exhalation,

and means for providing a system electrical signal by superimposing saidseries of pulse signals upon said third signal such that said series ofpulse signals occur during the time an inhalation occurs.

2. The invention according to claim 1 wherein said integrating meansincludes multiplying means for multiplying said first and secondelectrical signals prior to integrating the product thereof.

3. The invention according to claim 1 wherein said pulse generator meansincludes memory means for storing a value equal to the peak percent ofnitrogen during each exhalation and delay means for providing said pulsegenerator means signal during the next inhalation.

4. The invention according to claim 3 wherein said next exhalation isdetected by means determining that said second signal is below a certainvalue.

5. The invention according to claim 3 wherein said second signal is ananalog signal having an instantaneous magnitude related to theinstantaneous percent of nitrogen during each exhalation and whereinsaid memory means includes a capacitor which is charged to a voltagerelated to the maximum magnitude of said second signal.

6. The invention according to claim 5 wherein said pulse generatingmeans include means for discharging said capacitor by determining thatthe instantaneous magnitude of said second signal is below a certainvalue.

7. The invention according to claim 1 wherein said system furtherincludes minimum flow detector means for determining when said firstsignal is below a predetermined value and minimum percent nitrogendetector means for determining when said second signal is below apredetermined value, said integrating means being inhibited fromproviding a signal whenever said first or said second signals are lessthan said predetermined values therefor, and said pulse generating meansbeing inhibited from providing a signal whenever said second signal isbelow said predetermined value therefor.

8. The invention according to claim 7 wherein said integrating meansincludes multiplying means for multiplying said first and second signalsprior to integrating the product thereof.

9. The invention according to claim 8 wherein said integrating meansfurther includes inhibiting means for inhibiting said integrating meansfrom integrating the product of said first and second signals whenevereither of said first or second signals is less than said predeterminedvalue therefor.

10. A pulmonary testing system for providing an electrical signalcapable of being transmitted over a single pair of telephone lines to arecording device for causing, in response to said transmitted signal, agraphic representation of the peak percent of nitrogen expired by aperson during each one of a plurality of successive breaths, and thetotal volume of nitrogen expired by said person during said plurality ofbreaths, said person, during said plurality of breaths, inhaling agaseous mixture containing negligible nitrogen and exhaling a gaseousmixture containing a decreasing percent of nitrogen, said systemcomprising:

means responsive to said plurality of successive breaths for providing afirst electrical signal having an instantaneous magnitude proportionalto the instantaneous gas flow resulting from said breaths,

analyzer means responsive to said plurality of successive breaths forproviding a second electrical signal having an instantaneous magnitudeproportional to the instantaneous percent of nitrogen contained in eachexhalation, multiplying means responsive to said first and secondsignals for multiplying said first signal times said second signal toprovide a nitrogen flow signal,

integrating means responsive to said nitrogen flow signal forintegrating said nitrogen flow signal to provide a signal indicating thetotal volume of nitrogen expired by said person, pulse generating meansresponsive to said second signal for providing one pulse for eachexhalation, said pulse having a magnitude proportional to the largestmagnitude of said second signal during that exhalation, said pulse beingprovided during the inhalation immediately following that exhalation,

and output means to which is applied said pulse generating means signaland said integrating means signal for adding said signals appliedthereto, thereby providing said system electrical signal.

11. The invention according to claim 10 wherein said output meansfurther includes transmitting means which, in response to said addedsignals, provides a modulated signal as said system electrical signal.

12. The invention according to claim 10 wherein said system furtherincludes minimum detector means for determining whether said firstsignal is above a first minimum magnitude and whether said second signalis above a second minimum magnitude, said minimum detector meansincluding means causing said multiplying means to be inhibited fromproviding a signal whenever either of said first or second signals has amagnitude below said respective first and second minimum magnitudes.

13. The invention according to claim 12 wherein said minimum detectormeans includes means for inhibiting said pulse generating means fromproviding a signal whenever said second signal has a magnitude belowsaid second minimum magnitude.

14. The invention according to claim 10 wherein said system furtherincludes means for providing a second system electrical signal whichrepresents the spirometry data of a single breath of said person.

15. The invention according to claim 14 wherein said system furtherincludes switching means to select between said first and second systemelectrical signals,

and wherein said system further includes transmitter means to which theselected one of said first and second system electrical signals isapplied for providing a modulated signal representative of said selectedsignal to a single pair of telephone lines.

16. The invention according to claim wherein said pulse generating meansincludes a storage capacitor for storing electrical energy having avoltage proportional to the highest magnitude of said second signalduring each breath, and logic means responsive to said second signalbeing below a certain magnitude to cause said pulse to be providedduring said immediately following inhalation.

17. The invention according to claim 16 wherein said pulse generatingmeans further includes switching means responsive to said logic meansfor causing said capacitor to discharge after said pulse is provided andbefore the immediately following exhalation.

18. Circuitry for transmission of pulmonary information from a testlocation to a remote location by means of a telephone circuitcomprising:

a conduit adapted for communication with the respiratory system of apatient, I

a flowmeter joined to the conduit, the flowmeter having an electricaloutput,

a percent nitrogen analyzer joined to the conduit and having anelectrical output,

a multiplier connected to the electrical output of the flowmeter,

a minimum flow detector connected to the output of the flowmeter,

'a peak percent nitrogen follower,

a minimum percent nitrogen detector,

means connecting the output of the percent nitrogen analyzer to themultiplier and to the peak percent nitrogen follower and to the minimumpercent nitrogen detector,

a gate member,

means connecting the outputs of the multiplier and the minimum flowdetector and the minimum percent nitrogen detector to the gate member,

a percent nitrogen pulse generator including time delay means,

means connecting the output of the minimum percent nitrogen detector tothe peak percent nitrogen follower and to the percent nitrogen pulsegenerator,

a transmitter,

means connecting the time delay means to the transmitter and to the peakpercent nitrogen follower,

an integrator,

means connecting the output of the gate member to the integrator,

means connecting the output of the integrator to the transmitter, acentral unit including a demodulator and a recorder,

means for connecting the transmitter and the demodulator to a telephonecircuit at opposite portions thereof,

means connecting the output of the demodulator to the recorder,

the transmitter thus transmitting to the central unit signalsrepresentative of the peak percent nitrogen expired by a patient in eachbreath and the nitrogen volume in each breath of the patient.

19. The system of claim 10 in which the analyzer means comprises: a highoutput impedance circuit which includes first operational amplifyingmeans, the first operational amplifying means being an invertingamplifying means and having an input and an output,

means including first unidirectional current conducting means forcoupling from the output thereof to the input of said first operationalamplifying means,

second unidirectional current conducting means,

second operational amplifying means, the second operational amplifyingmeans being high input impedance operational amplifying means and havinga noninverting input and an output, said output being coupled to theinput of said first amplifying means, and

means for connecting the input of said first operational amplifyingmeans through said second unidirectional current conducting means to theoutput of said first operational amplifying means so that current flowsfrom the input of said second operational amplifying means to the outputof said first operational amplifying means.

20. The invention according to claim 19 wherein each of said first andsecond unidirectional current conducting means is the base-emitterjunction of a transistor.

21. The invention according to claim 19 wherein said second operationalamplifying means further has an inverting input coupled to the output ofsaid second operational amplifying means.

22. The invention according to claim 19 wherein the output of saidcircuit is the junction of said second operational amplifying means andsaid second unidirectional current conducting means.

1. A pulmonary testing system for providing an electrical signalindicating the peak percent nitrogen expired by a person in a breath andthe total nitrogen volume expired by said person during repetitiousbreathing comprising: means responsive to said person''s repetitiousbreathing for providing a first electrical signal proportional to thegas flow in each expired breath, analyzer means responsive to therepetitious exhaling of said person for providing a second electricalsignal indicating the percent of nitrogen during each exhalation,integrating means responsive to said first and second electric signalsfor providing a third electrical signal indicating the total volume ofnitrogen exhaled by said person, pulse generator means responsive tosaid second signal for providing a series of pulse signals, each pulsesignal indicating the peak percent of nitrogen during a singleexhalation, and means for providing a system electrical signal bysuperimposing said series of pulse signals upon said third signal suchthat said series of pulse signals occur during the time an inhalationoccurs.
 2. The invention according to claim 1 wherein said integratingmeans includes multiplying means fOr multiplying said first and secondelectrical signals prior to integrating the product thereof.
 3. Theinvention according to claim 1 wherein said pulse generator meansincludes memory means for storing a value equal to the peak percent ofnitrogen during each exhalation and delay means for providing said pulsegenerator means signal during the next inhalation.
 4. The inventionaccording to claim 3 wherein said next exhalation is detected by meansdetermining that said second signal is below a certain value.
 5. Theinvention according to claim 3 wherein said second signal is an analogsignal having an instantaneous magnitude related to the instantaneouspercent of nitrogen during each exhalation and wherein said memory meansincludes a capacitor which is charged to a voltage related to themaximum magnitude of said second signal.
 6. The invention according toclaim 5 wherein said pulse generating means include means fordischarging said capacitor by determining that the instantaneousmagnitude of said second signal is below a certain value.
 7. Theinvention according to claim 1 wherein said system further includesminimum flow detector means for determining when said first signal isbelow a predetermined value and minimum percent nitrogen detector meansfor determining when said second signal is below a predetermined value,said integrating means being inhibited from providing a signal wheneversaid first or said second signals are less than said predeterminedvalues therefor, and said pulse generating means being inhibited fromproviding a signal whenever said second signal is below saidpredetermined value therefor.
 8. The invention according to claim 7wherein said integrating means includes multiplying means formultiplying said first and second signals prior to integrating theproduct thereof.
 9. The invention according to claim 8 wherein saidintegrating means further includes inhibiting means for inhibiting saidintegrating means from integrating the product of said first and secondsignals whenever either of said first or second signals is less thansaid predetermined value therefor.
 10. A pulmonary testing system forproviding an electrical signal capable of being transmitted over asingle pair of telephone lines to a recording device for causing, inresponse to said transmitted signal, a graphic representation of thepeak percent of nitrogen expired by a person during each one of aplurality of successive breaths, and the total volume of nitrogenexpired by said person during said plurality of breaths, said person,during said plurality of breaths, inhaling a gaseous mixture containingnegligible nitrogen and exhaling a gaseous mixture containing adecreasing percent of nitrogen, said system comprising: means responsiveto said plurality of successive breaths for providing a first electricalsignal having an instantaneous magnitude proportional to theinstantaneous gas flow resulting from said breaths, analyzer meansresponsive to said plurality of successive breaths for providing asecond electrical signal having an instantaneous magnitude proportionalto the instantaneous percent of nitrogen contained in each exhalation,multiplying means responsive to said first and second signals formultiplying said first signal times said second signal to provide anitrogen flow signal, integrating means responsive to said nitrogen flowsignal for integrating said nitrogen flow signal to provide a signalindicating the total volume of nitrogen expired by said person, pulsegenerating means responsive to said second signal for providing onepulse for each exhalation, said pulse having a magnitude proportional tothe largest magnitude of said second signal during that exhalation, saidpulse being provided during the inhalation immediately following thatexhalation, and output means to which is applied said pulse generatingmeans signal and said integrating means signal for adding said signalsapplied thereto, thereby proviDing said system electrical signal. 11.The invention according to claim 10 wherein said output means furtherincludes transmitting means which, in response to said added signals,provides a modulated signal as said system electrical signal.
 12. Theinvention according to claim 10 wherein said system further includesminimum detector means for determining whether said first signal isabove a first minimum magnitude and whether said second signal is abovea second minimum magnitude, said minimum detector means including meanscausing said multiplying means to be inhibited from providing a signalwhenever either of said first or second signals has a magnitude belowsaid respective first and second minimum magnitudes.
 13. The inventionaccording to claim 12 wherein said minimum detector means includes meansfor inhibiting said pulse generating means from providing a signalwhenever said second signal has a magnitude below said second minimummagnitude.
 14. The invention according to claim 10 wherein said systemfurther includes means for providing a second system electrical signalwhich represents the spirometry data of a single breath of said person.15. The invention according to claim 14 wherein said system furtherincludes switching means to select between said first and second systemelectrical signals, and wherein said system further includes transmittermeans to which the selected one of said first and second systemelectrical signals is applied for providing a modulated signalrepresentative of said selected signal to a single pair of telephonelines.
 16. The invention according to claim 10 wherein said pulsegenerating means includes a storage capacitor for storing electricalenergy having a voltage proportional to the highest magnitude of saidsecond signal during each breath, and logic means responsive to saidsecond signal being below a certain magnitude to cause said pulse to beprovided during said immediately following inhalation.
 17. The inventionaccording to claim 16 wherein said pulse generating means furtherincludes switching means responsive to said logic means for causing saidcapacitor to discharge after said pulse is provided and before theimmediately following exhalation.
 18. Circuitry for transmission ofpulmonary information from a test location to a remote location by meansof a telephone circuit comprising: a conduit adapted for communicationwith the respiratory system of a patient, a flowmeter joined to theconduit, the flowmeter having an electrical output, a percent nitrogenanalyzer joined to the conduit and having an electrical output, amultiplier connected to the electrical output of the flowmeter, aminimum flow detector connected to the output of the flowmeter, a peakpercent nitrogen follower, a minimum percent nitrogen detector, meansconnecting the output of the percent nitrogen analyzer to the multiplierand to the peak percent nitrogen follower and to the minimum percentnitrogen detector, a gate member, means connecting the outputs of themultiplier and the minimum flow detector and the minimum percentnitrogen detector to the gate member, a percent nitrogen pulse generatorincluding time delay means, means connecting the output of the minimumpercent nitrogen detector to the peak percent nitrogen follower and tothe percent nitrogen pulse generator, a transmitter, means connectingthe time delay means to the transmitter and to the peak percent nitrogenfollower, an integrator, means connecting the output of the gate memberto the integrator, means connecting the output of the integrator to thetransmitter, a central unit including a demodulator and a recorder,means for connecting the transmitter and the demodulator to a telephonecircuit at opposite portions thereof, means connecting the output of thedemodulator to the recorder, the transmitter thus transmitting to thecentral unit signals represeNtative of the peak percent nitrogen expiredby a patient in each breath and the nitrogen volume in each breath ofthe patient.
 19. The system of claim 10 in which the analyzer meanscomprises: a high output impedance circuit which includes firstoperational amplifying means, the first operational amplifying meansbeing an inverting amplifying means and having an input and an output,means including first unidirectional current conducting means forcoupling from the output thereof to the input of said first operationalamplifying means, second unidirectional current conducting means, secondoperational amplifying means, the second operational amplifying meansbeing high input impedance operational amplifying means and having anoninverting input and an output, said output being coupled to the inputof said first amplifying means, and means for connecting the input ofsaid first operational amplifying means through said secondunidirectional current conducting means to the output of said firstoperational amplifying means so that current flows from the input ofsaid second operational amplifying means to the output of said firstoperational amplifying means.
 20. The invention according to claim 19wherein each of said first and second unidirectional current conductingmeans is the base-emitter junction of a transistor.
 21. The inventionaccording to claim 19 wherein said second operational amplifying meansfurther has an inverting input coupled to the output of said secondoperational amplifying means.
 22. The invention according to claim 19wherein the output of said circuit is the junction of said secondoperational amplifying means and said second unidirectional currentconducting means.